HELP! Find the domain of the graphed function

The function show two sisters' savings account and the rate at which they plan to deposit money

Which is the correct first step in finding the area of the base of a cylinder with a volume of 26x cubic meters and a height of 6.5 meters? v=bh 6.5=b(26x) v=bh v=26pi+(6.5) v=bh v=26pi(6.5) v=bh 26pi=b(6.5)

What is the period of the sinusoidal function ?